A wound string would be your best bet. Much thinner than an unwound one. My personal recommendation would be a Thomastik Infeld CF30 or, failing that, a Fremont Soloist.
I'm using a Freemont (wound) low g string on a LoPrinzi concert, & that's working well.
I've found that Donna is good about answering questions, (in my case, even though I didn't buy directly from her), so if you'd like her input, you might want to contact her, I used the email address on her website.
A wound string would be your best bet. Much thinner than an unwound one. My personal recommendation would be a Thomastik Infeld CF30 or, failing that, a Fremont Soloist.
The Living Waters Fluorocarbon Low-G is pretty thin as well. Thinner than the wound strings I have encountered. I don't have a pack nearby to give the specific diameter, but it's on the outside of the package.
D'addario normal tension silver wound classical guitar 4th string is 0.74mm.
I'd be extremely surprised to find a wound low g that was a higher gauge than an unwound - the primary reason for wound strings is to keep the gauge low but the tension high enough. What wounds have you been using? Most guitar 5th strings are around 0.9mm, i.e. the same as the living water low g, so have you been using the 6th string as a low g? That would be seriously floppy tension, I just can't imagine it working.
The Living Waters Fluorocarbon Low-G is pretty thin as well. Thinner than the wound strings I have encountered. I don't have a pack nearby to give the specific diameter, but it's on the outside of the package.